1. Technical Field
The present invention relates to a multiple-light-type vehicle headlamp system including a headlamp, the headlamp being constructed of a plurality of lamp units housed in a lamp chamber, or a headlamp formed from one or more lamp units housed in a lamp chamber as well as from an auxiliary lamp disposed in the vicinity of the headlamp. More specifically, the present invention relates to a vehicle headlamp system constructed such that the quantity of light emitted ahead of a vehicle is controlled by subjecting the quantity of light radiated from at least one lamp unit to dimming control in the former case in accordance with the driving conditions, or by subjecting the quantity of light radiated from at least one lamp unit and/or the auxiliary lamp to dimming control in the latter case in accordance with the driving conditions.
2. Background of the Related Art
In the related art, a vehicle headlamp system is constructed to enable selective switching between a low-beam light distribution pattern and a high-beam light distribution pattern. The related art vehicle headlamp system having a fixed configuration of the respective low and high light distribution patterns encounters difficulty in emitting a beam in an appropriate light distribution pattern in accordance with driving conditions.
For this reason, as described in, Japanese publication JP-UM-A-2-17364, the contents of which is incorporated herein by reference, a proposed vehicle headlamp system emits a beam in a light distribution pattern corresponding to the driving conditions, by causing lamp units to illuminate in an appropriate combination corresponding to the driving conditions. In this related art system, a lamp body houses multiple lamp units that emit beams ahead of a vehicle in a predetermined light distribution pattern.
Moreover, Japanese publication JP-A-11-45606, the contents of which is incorporated herein by reference, discloses a proposed related art vehicle headlamp system that enables an increase or decrease in the quantity of light radiated from the respective lamp units housed in the lamp body through the driver's manual operation.
However, in the foregoing related art vehicle headlamp system, some of the lamp units are extinguished or re-illuminated in accordance with the driving conditions. Therefore, there arises a problem of the chance of the driver feeling uncertainty due to a sudden drop in the driver's view field, or the chance of drivers of oncoming vehicles or pedestrians feeling uncertainty (e.g., a false recognition of occurrence of passing operation). For example, but not by way of limitation, when the vehicle is viewed from the outside, some of the lamp units are suddenly extinguished and be come partially dark. Therefore, there also arises a problem of poor appearance of the lamp.
As shown in Japanese publication JP-A-2001-270383, the contents of which is incorporated herein by reference, a solution to “the driver of interest, drivers of oncoming vehicles, and pedestrians feeling uncertainty” and a “a partial drop in the internal light of the lamp body deteriorating the appearance of the lamp” is proposed by configuring a vehicle headlamp system so that the quantity of light of at least some of the plurality of lamp units housed in the lamp body can be adjusted by dimming means and, in accordance with the driving conditions (e.g., the amount of rotation of a steering wheel as detected by a steering angle sensor), a control unit automatically drives the dimming means, to increase or decrease the quantity of light radiated from a predetermined lamp unit.
However, in the foregoing related art technique, the headlamp system performs dimming control such that the auxiliary lamp unit gradually shifts from a steady illuminated state to an extinguished state by housing, in a lamp body, an auxiliary lamp unit, such as a bend lamp or a cornering lamp, along with a high beam lamp unit and a low beam lamp unit, and gradually decreasing the amount of power (an effective value of an applied voltage, hereinafter called an “applied voltage”) fed to a light source (a halogen valve) of the auxiliary lamp unit in accordance with the driving conditions (e.g., the amount of rotation of a steering wheel). However, such a configuration induces a related art problem of deformation of a filament of the valve (i.e., the halogen valve) of the auxiliary lamp unit to be dimmed, thereby shortening the life of the valve.
To determine, the cause of this related art problem, an H8 valve (having a normal rated power of 12 volts and 35 watts) was subjected to a continuous illumination test, a blinking test (simple blinking, dimming performed at the time of extinction), and a voltage switching illumination test. Results such as those shown in FIGS. 9 and 10 were obtained.
Further, as shown in FIG. 11A, in the simple blinking test in which feeding power to the valve and suspension of power feed were alternately performed at intervals of five seconds (a voltage of 14 volts and a voltage of 0 voltage were applied to the filament of the valve at intervals of five seconds), the life of the valve (a feeding time accumulated until a rupture occurs) dropped slightly as shown in FIGS. 9 and 10 (a). However, for continuous illumination in which a given voltage (14 volts) is continuously applied to the valve, no deformation in the filament was observed.
As shown in FIG. 11B, in the blinking test (a dimming operation performed at the time of extinction) in which feeding power to the filament and suspension of power feed were alternately performed at intervals of five seconds to gradually decrease the amount of power (applied voltage) over a period of about two seconds (one second or 0.5 seconds) during suspension of power feed, thereby shifting the valve to an extinguished state, the filament was deformed as shown in FIGS. 9 and 10 (b). The life of the valve was shortened. Particularly, the lower the dimming speed (i.e., the longer the filament is cooled), the greater the deformation of the filament, and the shorter the life of the valve.
As shown in FIG. 11C, in the voltage switching illumination test in which alternating power supply was fed to the valve such that the voltage applied to the valve was switched between 14 volts and 6 (7, 8, 9, 9.5, and 10) volts at intervals of five seconds, when alternating power supply involving a minimum applied voltage of 6 volts (7 volts, 8 volts, 9 volts or 9.5 volts) was fed as shown in FIGS. 9 and 10C, the filament was deformed. In contrast, when the alternating power (14 volts/10 volts) involving a minimum applied voltage of 10 volts was fed, no substantial deformation in the filament was observed.
Deformation of the filament (i.e., the degree of deformation, a time which lapses until deformation arises, and influence on the life time of the valve) became increasingly severe as the minimum applied voltage increased in a sequence of: 6 volts, 7 volts, 8 volts. Particularly, for the minimum applied voltage of 8 volts, the deformation was considerable.
When the minimum applied voltage was increased in the sequence of: 8 volts, 9 volts, 9.5 volts, the degree of deformation became weak, and the life of the valve was prolonged. Here, the accumulated time during which 14 volts had been supplied was taken as the life of the voltage switching illumination test.
Since difficulty is encountered in directly measuring the temperature of the filament that is achieved at the time of illumination of the valve, a radiant intensity of infrared rays of the illuminating filament was determined as a temperature distribution of the filament. Results shown in FIG. 12 were obtained FIG. 12A shows measurement points P1 to P18 on the filament. FIG. 12B shows the temperature distribution of the filament achieved with applied voltages 6, 8, 10, 12, 14, and 16, while the radiant intensity of infrared rays achieved at an applied voltage of 14 volts was taken as 100%. The highest temperature is achieved at the longitudinal center of the filament, and the temperature decreases toward ends of the filament.
FIGS. 13A and 13B show variations in the temperature of the filament achieved during the simple blinking test, the blinking (light is dimmed at the time of extinction) test, the blinking (light is dimmed to a threshold value at the time of extinction) test, and the voltage switching illumination test. FIG. 13A shows variations in temperature of filament having arisen after simple blinking, blinking (dimming during extinction), blinking (dimmed to threshold value during extinction as in embodiment). FIG. 13B shows variations in temperature of filament having arisen after simple blinking and voltage switching.
As shown in FIG. 13A, according to the blinking test (dimming performed for extinction) the longer the dimming time (0.5 seconds→one second→two seconds), the more slowly the filament is cooled. In the voltage switching illumination test in FIG. 13B, the cooling speed of the filament achieved immediately after switching from the maximum applied voltage to the minimum voltage is fast. However, the temperature of the filament slowly, gradually approaches the temperature to be achieved by the minimum applied voltage (i.e., the cooling speed of the filament is reduced).
In the blinking (light is dimmed at the time of extinction) test (see FIGS. 9, 10, 11, and 13B), the state of deformation of the filament was captured by a camera, and deforming motions were examined. As shown in FIGS. 14A and 14B, the filament axially expanded and contracted and vibrated every time the valve was illuminated. Some of the adjacent coil sections contacted each other, thereby causing pitch touch. Specifically, both end sections of the filament are fixedly fused to, e.g., a lead support.
Due to electromagnetic force generated by a rush current flowing during illumination of the valve and the thermal stress caused by a temperature variation, the filament axially expanded and contracted (i.e., vibrated) and was subjected to repetition of axial expansion and contraction, thereby resulting in deformation. One possible reason for this effect is that the mechanical strength of a portion of the filament has become weak: that apart of the filament having low strength is deformed by expansion and contraction of the coil and that coil sections c1, c1 adjoining to the deformed area come into contact with each other, thereby causing pitch touch and rupture.
From the foregoing test results, the applicant has made the following determinations. The filament is made of high purity tungsten. From room temperature to a high temperature, the basic crystalline structure of tungsten is a body-centered cubic lattice. Tungsten is not known to have-any definite transition point (or transition temperature) at which the crystalline structure changes. However, the test results become understandable if a transition point (transition temperature) at which a change arises in the crystalline structure of a tungsten filament roughly corresponds to a light source applied voltage of 8 volts (i.e., the temperature of the filament achieved when a voltage of 8 volts is applied to the valve).
More specifically, every time a dimming control operation is performed for shifting the valve to an extinguished state by gradually decreasing the amount of power fed to the valve (i.e., the voltage applied to the light source) during illumination, the tungsten filament is gradually cooled from a temperature higher than the transition point (the transition temperature). Every time the filament is cooled, the transition point (transition temperature) unique to the filament tungsten is gradually passed. If the transition point (transition temperature) is repeatedly passed in association with dimming control operation while tungsten is gradually cooled, the crystalline structure of tungsten is changed to a structure readily deformed by stress (i.e., the transition distribution in a crystal is changed) achieved at the time of annealing of the crystalline structure of tungsten. Consequently, the filament is presumed to be deformed by the electromagnetic force or thermal stress caused during illumination of the valve.
As shown in FIGS. 9, 10, and 13B, the influence of “annealing achieved at the transition point (transition temperature)” is significant when a dimming speed (a cooling speed of the filament) is slow. As shown in FIGS. 9, 10, and 13A, in the simple blinking test not involving a dimming operation, the speed at which the filament is annealed is rapid. Hence, the filament is considered less susceptible to the influence of “annealing achieved at the transition point (transition temperature)” (i.e., the influence on the crystalline structure).
The voltage switching illumination test involving application of alternating power supply was conducted for examining alight source applied voltage corresponding to the transition point (transition temperature). As shown in FIGS. 9 and 10 (c), when the minimum applied voltage is 7 to 8 volts, shortening of the valve life (≈a deformation of the filament) is considerable. The filament of this case is affected by the annealing operation achieved at the transition point (transition temperature) during the course of the filament shifting from a high-temperature state in which a high heating value is obtained as a result of application of a voltage of 14 volts, to a low-temperature state in which a low heating value is obtained as a result of application of the minimum voltage (during the course of the applied voltage being changed).
Specifically, the cooling speed of the filament achieved immediately after the applied voltage has been switched from 14 volts to 7 to 8 volts is fast. However, after a while, the temperature of the filament slowly approaches the temperature corresponding to the heating value achieved at the applied voltage of 7 to 8 volts. At this time, the transition point is passed slowly, whereupon the filament is affected by the annealing operation achieved at the transition point (transition temperature).
Even if the transition point (transition temperature) is situated in the vicinity of the light source applied voltage of about 8 volts, the temperature distribution of the filament is such that the ends and the center of the filament show a difference of 200° C. As a matter of course, when an alternating power supply involving a minimum applied voltage of 7 or 9 volts (14 volts/7 volts or 14 volts/9 volts) is applied to the filament, the filament is slightly affected by the “annealing operation achieved at the transition point (transition temperature).” This result also applies when an alternating power supply involving a minimum applied voltage of 6 and 9.5 volts (14 volts/6 volts or 14 volts/9.5 volts) is applied to the filament.
When an alternating power supply involving a minimum applied voltage of 6 volts (14 volts/6 volts) is applied to the filament, the cooling speed of the filament (i.e., a temperature variation) achieved when the transition point (transition temperature) is passed is considerably fast. Therefore, when compared with a case where the alternating power supply (14 volts/7 volts) is applied to the filament, the extent to which the filament is affected by the annealing operation achieved at the transition point (transition temperature) is smaller. When the alternating power supply involving a minimum applied voltage of 10 volts (14 volts/10 volts) is applied to the filament, the entire filament fails to reach the transition point (transition temperature), and hence the filament is considered not affected by the annealing operation achieved at the transition point (transition temperature).
As mentioned above, on the premise that the transition point (transition temperature) of a filament made of tungsten is present within the valve applied voltage range from 7 to 8 volts (the temperature range of the filament achieved when a voltage of 7 to 8 volts is applied to the valve), applicant has considered that the filament would not be affected by the annealing operation achieved at the transition point (transition temperature) within the range of a light source applied voltage of 14 to 9 volts at which the transition point (transition temperature) is not achieved even when dimming control operation is performed to gradually decrease the light source applied voltage, and that the filament would not be affected by the annealing operation achieved at the transition point (transition temperature) within the range of a light source applied voltage of 9 volts or less at which the transition point (transition temperature) is passed, so long as the filament is rapidly cooled by means of decreasing the light source applied voltage to 0 in one stroke (i.e., substantially instantaneously), as discovered by applicant.
As shown in FIG. 11D, there was adopted, as dimming control for extinguishing light by gradually decreasing the amount of power supplied to the valve (i.e., the light source applied voltage), a configuration for controlling the light source applied voltage to 0 in one stroke when a predetermined threshold value (e.g., 9 volts) is achieved by means of gradually decreasing the light source applied voltage from 14 volts to the predetermined threshold value (9 volts) at which the transition point is not achieved, over a period of one to two seconds. Through repetition of the blinking test (dimming performed at the time of extinction), prevention of deformation of the filament is ascertained to be effective. The presently claimed invention has been proposed on the basis of this concept.